1. Field of the Invention
The present invention relates to a hydrostatic stepless transmission (hereinafter, referred to as “HST”) including a hydraulic pump, a hydraulic motor and a center section, wherein the hydraulic pump and motor are mounted on the center section and are fluidly connected to each other through a pair of fluid passages formed in the center section.
2. Related Art
A typical conventional integral hydrostatic transaxle, i.e., IHT, includes a transaxle housing incorporating a HST and an axle, wherein hydraulic pump and motor, constituting the HST, are mounted on a center section so as to have respective rotary axes perpendicular to each other. When this NT is installed in a vehicle, e.g., a mower tractor, having a vertical crankshaft engine, typically, a vertical pump shaft serving as the rotary axis of the hydraulic pump is drivingly connected to an engine output shaft through a belt transmission.
The engine of the mower tractor is desired to be lowered to have a low center of gravity so that the mower tractor can travel stably. However, a sufficient ground clearance must be ensured even if the IHT drivingly connected to the vertical crankshaft engine through the belt transmission is lowered to correspond to the lowered engine. For example, it is suggested that the center section is vertically thinned to ensure the sufficient ground clearance under the lowered IHT. However, the IHT is also desired to be horizontally minimized. Thus, the center section is desired to be minimized vertically as well as horizontally. To achieve such a center section, how to shape the fluid passages in the center section is significant.